Radio-frequency-energy transmission line and antenna



Dec. 29, 1959 LAN JEN CH RADIO-FREQUENCY-ENERGY TRANSMISSION LINE'ANDANTENNA Filed April 15. 1955 FIG. 3

INVENTOR. LAN JEN CHU A TTORNEYS United States PatentRADIO-FREQUENCY-ENERGY TRANSMISSION LINE AND ANTENNA Lan Jen Chu,Lexington, Mass.

Application April 15, 1955, Serial No. 501,570

'4 Claims. (Cl. 343-810) The present invention relates toradio-frequency-energy transmission lines and antennas, and, moreparticularly, to transmission lines and antennas that are especiallyadapted for use in the high and ultra-high-frequency bands.

Various transmission lines and antennas of special configuration haveheretofore been evolved in an attempt not only to reduce themanufacturing and maintenance cost of the transmission-line and antennastructures, but, also, to render such structures more efficient. As anillustration, it has been proposed to simplify conventional coaxial orparallel-wire transmission lines through the expedient of printing ordepositing conductor strips upon opposite sides of a dielectric layer.This proposal, as well as many others, however, is subject to severaldisadvantages. In the first place, the velocity of propagation of theradio-frequency energy along such transmission lines is considerablyless than the very desirable free-space velocity of electromagneticenergy in air, that is, the velocity of light. This is because theradio-frequency energy must travel through the medium of the dielectricsupport for the two conductors of the transmission line or antennasystem. In addition, the radio-frequency energy is subject toappreciable attenuation as a result of losses occurring in the saiddielectric medium.

An object of the present invention, accordingly, is to provide a new andimproved transmission line and antenna structure that, unlike thebefore-mentioned priorart transmission lines and antenna systems,permits the radio-frequency energy to travel with substantially thevelocity of light and with substantially no attenuation.

An additional object is to provide such a transmissionline and antennastructure that, though particularly adapted for balanced-line operation,can easily be designed to have any desired impedance characteristics.

Still a further object is to reduce the manufacturing and maintenancecosts of transmission lines and antennas.

Other and further objects will be explained hereinafter and will be moreparticularly pointed out in the appended claims.

The invention will now be described in connection with the accompanyingdrawings, Fig. 1 of which is a fragmentary perspective view illustratinga preferred form of the present invention as applied to a transmissionline;

Fig. 2 is an exploded view illustrating the application of thetransmission-line structure of Fig. 1 to a preferred antenna;

Fig. 3 is a fragmentary perspective view of the assembled antenna ofFig. 2 encased within a tubular housing; and

Figs. 4 and 5 are fragmentary views of modifications.

Referring to Fig. 1, a balanced two-conductor transmission line is showncomprising a pair of opposing substantially planar similar conductors 1and 3 extending longitudinally along the inner surfaces 5 and 7 of apair of dielectric-sheet supports 9 and 11. The supports 9 and 11 mayassume the form of Bakelite, fiberfilass or other dielectric sheets orlayers and the planar conductors 1 and 3 may be of sheet copper or brassand the like, attached at 13 as by cementing or gluing along the innersurfaces 5 and 7 of the dielectric supports 9 and 11. If desired, theconductor strips 1 and 3 may also be sprayed or printed upon thesurfaces 5 and 7 of the dielectric-layer supports 9 and 11. Thedielectric supports 9 and 11 are positioned substantially parallel toone another with the conductors 1 and 3, which are substantiallyco-planar with the respective surfaces 5 and 7 of the supports 9 and 11,disposed in capacitive opposition. Radio-frequency energy may be appliedto the left-hand terminals of the conductors 1 and 3 and propagatedalong the two-conductor balanced transmission line formed by theconductors 1 and 3, the radio-frequency energy being guided between theopposing inner faces of the planar conductors 1 and 3.

In accordance with the present invention, this radiofrequency energyguided in the space between the planar conductors 1 and 3 is permittedto travel with substantially the velocity of light. This end is achievedby utilizing a dielectric spacer 15 external to the space I between theconductors 1 and 3 so that the space I may be constituted solely of air.By displacing the spacer 15 away from the side edges of the conductors 1and 3, that energy which is guided at the side edges of the conductors 1and 3 may similarly travel in an air medium II. The spacer 15 ispreferably in the form of a honeycomb structure having cells of air andthat may be glued or otherwise secured to the inner surfaces 5 and 7 ofthe dielectric layers 9 and 11 in order rigidly to unite them. Theradio-frequency energy thus travels unimpeded through substantially anair medium com pletely along the transmission line, achieving thedesired advantageous end of permitting the energy to travel withsubstantially the velocity of light. The use of the preferably porousair-filled honeycomb structure 15, moreover, provides a minimum ofdielectric material in the path of stray field.

In addition, in accordance with the present invention, there isnegligible attenuation of the radio-frequency energ since there is nodielectric medium besides the air in the space I between, and the spaceII immediately to the side of, the conductors 1 and 3, and a minimumamount of dielectric material is present further to the side. Inaddition, the structure of the present invention is not subject to thereflections that give rise to undesirable standing-wave ratios and thatare inherent in prior transmission lines that require dielectric mediabetween the conductors or other dielectric supports therebetween. Thisresult is attained in Fig. 1, moreover, with an entirely symmetrical andbalanced-line feed. The ends of the structure, moreover, may be sealedover and it may be rendered air-tight or gasfilled with a gas at anydesired pressure. The simplicity of manufacture of the component partsand of assembly of the same provides, in addition, a relatively low-costarticle.

Transmission lines constructed in accordance with the present invention,furthermore, are adapted for simple adjustment to any desiredcharacteristic impedance. This may be easily accomplished, for example,merely by varying the spacing between the dielectric layers 9 and 11, asby utilizing honeycomb or other spacers 15 of different heights, or byvarying the relative widths of the conductors 1 and 3 as shown, forexample, in the embodiment of Fig. 4.

Not only is the structure of the present invention extremelyadvantageous as a transmission line, but it is of important utility,also, in connection with radiating or receiving antenna structures andparticularly those constituted of a number of antenna elements. In viewof the fact that the phase velocity of the radio-frequency energy guidedalong the line is substantially that of light because of theconstruction of the present invention, an antenna so constructed will beof extremely high gain. This is because the gain of an antenna isproportional to the ratio of the length of the antenna to the wavelengthin free space. The present invention thus renders the Wavelength alongthe antenna substantially equal to that of free space, thus providingmaximum gain conditions for the same number of antenna elements.In=addition to the before-mentioned results of extremely low-1attenuation, furthermore, an antennasystem so constructed is lesssubject to the type of standing-wave phenomena before-described.

As an illustration of the application of the transmission-line structureof the present invention to an antenna system, a beacon-type dipolearray antenna is shown in Fig. 2. The dielectric layers 9, 11 are thereshown spaced apart in order to illustrate the details of construction.Upon the surface 7, a main longitudinally extending planar conductor 3is mo'unted,.the width of the dielectric support 11 being wider thanthat of the conductor in order to permit the use of the spacerconnecting member 15. At intervals along the main planar conductor 3,there are provided a plurality of transverse branch conductors 2, 4, 6and 8. It is to be understood that more or less branch conductors thanthe four illustrated may, of course, be employed. The corresponding mainplanar longitudinally extending conductor 1 is shown secured to theinner surface 5 of the dielectric support 9 and is provided with similarrightangularly extending transverse branch planar conductors 10, 12, 14and 16. At each end of the transverse branch extensions 2, 4, 6 and 8are downwardly extending respective dipole-element planar conductors 22,24, 26 and 28. At the ends of the transverse conductors 10, 12, 14 and16 there are similarly provided upwardly extending dipole-element planarconductors 3 32, 34 and 36, respectively. When the dielectric supports 9and 11 are sandwiched together, with the honeycombed spacer material 15disposed therebetween in regions preferably external to the spaces I andII, for the reasons heretofore explained, a balanced dipole array isproduced having the before-mentioned advantages over present-day antennaarrays. of Fig. 2, the polarization of the radio frequency energy isvertical in view of the vertical orientation of the dipole elements. Thedipoles constituted of the elements 22 and 30, 24 and 32, 26 and 34, and28 and 36, may be successively spaced along the main-line conductors 1and 3 at intervals of, for example, awavelength of the energy for whichthe antenna was designed. It is pref erable for impedance-matchingpurposes that the width of the conductors 1 and 3 be successivelydecreased or reduced in the intervals between successive dipoles asshown at 13', 13 and 1"'3". Radio-frequency energy may be fed directlyto the bottom of the transmission lines 1 and 3 and a high-power gainradiation pattern, omni-directional in the horizontal plane, will beproduced which is highly suitable for radio-beacon purposes. If desired,this antenna may be enclosed in a tubular housing such as a radio-wavepermeable plastic cylinder 19, as of polystyrene, preferably end-sealedagainst the eifect of the atmosphere or pressurized with air or anyother gas media at any suitable pressure.

It is to be understood, of course, that the above-do scribed structureis equally useful as a receiving antenna and that many different typesof antenna elements and arrays may be constructed utilizing thetechnique herein disclosed.

As a typical illustration, an experimental line of the type illustratedin Fig. 1 having a pair of six-inch wide Fiberglas planar supports 9 and11 of about one thirtysecond of an inch thickness, separated byFiberglas honeycomb spacers 15 about a quarter of an inch in height,

In the system iii) and having copper-strip conductors l and 3 about oneinch wide and about 2 thousandths of an inch thick, glued to the innersurfaces 5 and 7, was found to propagate radio-frequency energy in theultra-high-frequency band with a phase velocity equal approximately toninety-five percent of the velocity of light. The characteristicimpedance of the line was about'fifty ohms and the losses along the linewere far less than those encountered with the prior-art strip-linesystems before-mentioned and other prior-art lines.

Another way of achieving the end of eliminating substantially alldielectric mountings or supports for a twoconductor transmission linefrom the radio-energy-propagating space between the conductors isillustrated in Fig. 5. The planar conductors 1 and 3 are there shownprovided with substantially co-planar right-angularly extendingextensions 21 and 23 which are secured to a planar dielectric support25. Actually, since there is some slight capacitance between theextensions 21' and 23 and the dielectric support 25 directly bounds thelower edges of the conductors 1 and 3, unlike the structures of Figs. 1to 4, a small quantity of radio energy will be propagated between theextensions 21 and 23 through the dielectric support 25. Substantiallyall of the radiofrequency energy, however, travels between the inneropposing faces of the substantially parallel planar conductors 1 and 3with almost the velocity of light and with low attenuation. As in thecase of the transmission lines of Figs. 1, 2 and 4-, the characteristicimpedance may easily be varied by, for example, adjustin the spacingbetween the planar transmission-line conductors 1 and 3 or by varyingthe dimensions of the same;

Further modifications will occur to those skilled in the art and allsuch are considered to fall Within the spirit and scope of the inventionas defined in the appended claims.

What is claimed is:

l. A radio-frequency-energy transmissionline'and" antenna having a pairof longitudinally extending'substantially planar main conductors eachprovided with aplurality of transverse planar branch conductorssubstantially co-planar with the main conductors connected at intervalstherealong and mounted upon the inner surfaces of a pair of spacedsubstantially parallel planar dielectric supports of greater transversedimension than the conductors, the conductors of the pair of conductorsand the corresponding branch conductors being disposed in opposition,and a plurality of longitudinally extending planar dipole-elementconductors mounted upon the inner surfaces of the supports at the endsof the branch conductors with the dipole elements mounted upon eachsupport extending in the opposite direction from the direction ofextension of the dipole elements mounted upon the other support of thepair of supports.

2. A radio-frequency-energy transmission line and antenna having a pairof longitudinally extending substantially planar main conductors eachprovided with a plurality of transverse planar branch conductorssubstantially co-planar with the main conductors connected at intervalstherealong and mounted upon the inner surfaces of a pair of spacedsubstantially parallel planar dielectric supports of greater transversedimension than the conductors, the conductors of the pair of conductorsand the corresponding branch conductors being disposed in oppositionwith the width of the portions of the main conductors between thesuccessive intervals therealong successively decreasing, and a pluralityof longitudinally extending planar dipole-element conductors mountedupon the inner surfaces of the supports at the ends of the branchconductors with the dipole elements mounted upon each support extendingin the opposite direction from the direction of extension of the dipoleelements mounted upon the other support of the pair of supports.

3. A radio-frequency-energy transmission line and antenna having a pairof longitudinally extending substantially planar main conductors eachprovided with a plurality of transverse planar branch conductorssubstantially co-planar with the main conductors connected at intervalstherealong and mounted upon the inner surfaces of a pair of spacedsubstantially parallel planar dielectric supports of greater trans-versedimension than the conductors, the conductors of the pair of conductorsand the corresponding branch conductors being disposed in oppositionwith the width of the portions of the main conductors between thesuccessive intervals therealong successively decreasing, a plurality oflongitudinally extending planar dipole-element conductors mounted uponthe inner surfaces of the supports at the ends of the branch conductorswith the dipole elements mounted upon each support extending in theopposite direction from the direction of extension of the dipoleelements mounted upon the other support of the pair of supports, andporous dielectric spacer means disposed between the supports.

4. A radio-frequency-energy transmission line and an tenna having a pairof longitudinally extending substantially planar main conductors eachprovided with a plurality of transverse planar branch conductorssubstantially co-planar with the main conductors connected at intervalstherealong and mounted upon the inner surfaces of a pair of spacedsubstantially parallel planar dielectric supports of greater transversedimension than the conductors, the conductors of the pair of conductorsand the corresponding branch conductors being disposed in oppositionwith the width of the portions of the main conductors between thesuccessive intervals therealong successively decreasing, a plurality oflongitudinally extending planar dipole-element conductors mounted uponthe inner surfaces of the supports at the ends of the branch conductorswith the dipole elements mounted upon each support extending in theopposite direction from the direction of extension of the dipoleelements mounted upon the other support of the pair of supports, andporous dielectric spacer means disposed between the supports in regionsexternal to the space between opposing conductors.

References Cited in the file of this patent UNITED STATES PATENTS2,556,224 Scott June 12, 1951 2,721,312 Grieg June 30, 1951 2,794,185Sichak May '28, 1957 2,800,634 Grieg July 23, 1957 2,819,452 Arditi eta1. Jan. 7, 1958 FOREIGN PATENTS 655,803 Great Britain Aug. 1, 1951

